The main research hypothesis for this study is that, among patients with Major Depressive Disorder (MDD) who have responded inadequately to treatment with SSRIs or SNRIs, the degree of improvement, as measured by the change from baseline of the Montgomery-Asberg Depression Rating Scale (MADRS)will be significantly greater among patients treated with EB-1010 (at the dose of 50 mg/day or 100 mg/day) than among those treated with placebo using the sequential parallel comparison design. The secondary research hypothesis for this study is that, among patients with MDD who have responded inadequately to treatment with SSRIs or SNRIs, the degree of improvement in depressive symptoms, as assessed by the MGH Cognitive and Physical Functioning Questionnaire (MGH CPFQ) will be significantly greater among those treated with EB-1010 (50 mg/day or 100 mg/day) than those treated with the SSRI paroxetine.